A triboelectric sensing yarn based on a negative Poisson's ratio structure and its preparation method

Abstract

A triboelectric sensing yarn based on a negative Poisson's ratio structure and its fabrication method are disclosed. This yarn, based on the principle of triboelectric nanogenerators, is used for real-time harvesting of mechanical energy from wearable smart fabrics and human motion. The negative Poisson's ratio triboelectric sensing yarn comprises a positive friction layer, a negative friction layer, and a conductive electrode layer. The conductive electrode layer is embedded within the positive / negative friction layers via coaxial wet spinning. The positive friction layer is wound around the surface of the negative friction layer through helical twisting, forming a negative Poisson's ratio structure. During stretching, the helix angle of the positive friction layer decreases, inducing radial expansion. This drives the negative and positive friction layers along a composite path of axial separation and radial sliding, ultimately resulting in the core layer and the winding layer exchanging positions. Through geometric coupling, the mechanical deformation energy is converted into continuous charge output. This design utilizes the negative Poisson's ratio effect to synergistically optimize the separation path and contact area of ​​the triboelectric layers, and can be used to fabricate flexible electronic sensing fabrics.

Description

Technical Field

[0001] This invention belongs to the field of energy harvesting technology, specifically relating to a triboelectric sensing yarn based on a negative Poisson's ratio structure and its preparation method. Background Technology

[0002] With the continuous growth in demand for health monitoring, wearable sensor technology has become a research hotspot in the fields of smart clothing, medical monitoring, and sports protection. Traditional sensors mostly exist in the form of external electronic devices, and the contradiction between their rigid structure and wearing comfort limits their deep integration with textiles. As a solution, smart yarns with sensing functions are gradually becoming the core carrier for the development of new smart clothing, the key being to achieve a balance between autonomous energy supply and flexible deformation. However, existing sensing yarns generally face technical bottlenecks such as low mechanical energy conversion efficiency and insufficient environmental adaptability, making it difficult to meet the needs of stable energy supply and multi-dimensional sensing under dynamic human activity.

[0003] Triboelectric nanogenerators, with their self-powered characteristics and high mechanical energy conversion efficiency, offer a new approach for the development of smart sensing yarns. Based on contact electrification and electrostatic induction coupling effects, this technology can directly convert low-frequency mechanical energy generated by human movement into electrical energy. However, traditional triboelectric fabrics are limited by planar contact modes, and under complex deformations such as bending and stretching, insufficient separation of the friction interface easily occurs, leading to a significant decrease in charge transfer efficiency. In addition, existing fibrous triboelectric devices mostly adopt a positive Poisson's ratio structure, and the lateral shrinkage effect under external force exacerbates the contact mismatch between friction layers, making it difficult to synergistically optimize energy conversion performance and mechanical durability.

[0004] In recent years, negative Poisson's ratio materials have attracted attention due to their unique mechanical response characteristics. When the material is subjected to axial tension, the negative Poisson's ratio lateral expansion effect can simultaneously increase the effective contact area of ​​the friction interface. This characteristic provides a theoretical possibility for solving the problems of low energy capture efficiency and poor fatigue resistance of traditional triboelectric yarns. However, existing technologies still face dual challenges in material system and structural design: on the one hand, traditional preparation processes make it difficult to achieve precise mechanical coupling of core-shell structures, and modulus differences between functional layers can easily lead to interface delamination; on the other hand, it is difficult to balance the biocompatibility and environmental stability of materials, which restricts their practical application in wearable scenarios. Against this background, developing novel triboelectric sensing yarns that combine high-efficiency energy conversion, adaptive deformation, and wearability comfort has become an urgent technological direction for breakthroughs in this field. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the present invention aims to provide a triboelectric sensing yarn based on a negative Poisson's ratio structure and its preparation method. Traditional triboelectric yarns experience a sharp drop in power generation efficiency when stretched due to the reduced contact area. This invention overcomes this limitation through a unique negative Poisson's ratio structure design. The yarn adopts an "internal and external synergistic" architecture: the inner layer is a conductive core composed of polyvinyl chloride and silver nanowires, ensuring efficient charge collection; the outer layer is a biocompatible triboelectric layer made of collagen and polyvinyl alcohol composite fibers, spirally wound to form a spring-like structure. This spiral winding process endows the yarn with negative Poisson's ratio characteristics. During stretching, the yarn expands laterally, causing the contact area between the inner and outer layers to dynamically increase with the amount of stretching, thereby significantly improving triboelectric power generation efficiency. Therefore, this triboelectric sensing yarn with a negative Poisson's ratio structure is suitable for scenarios requiring frequent deformation, such as smart fabrics and motion monitoring, enabling efficient collection of body mechanical energy. It also solves the energy supply problem of flexible electronic devices under stretching deformation.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A triboelectric sensing yarn based on a negative Poisson's ratio structure, comprising a core layer and a winding layer: The core layer and the winding layer are formed into a core-shell structure by coaxial wet spinning, and then wound at a spiral angle of 30°~60° through a spiral twisting process to form a spiral structure with negative Poisson bit properties. When stretched, the radial expansion effect of the spiral structure drives the increase of the contact area between the friction layers, realizing the conversion of mechanical energy into electrical energy.

[0007] Core layer: a negative triboelectric layer formed by combining polyvinyl chloride and a first conductive filler; Wrapping layer: a positive triboelectric layer formed by collagen aggregates, polyvinyl alcohol and a second conductive filler.

[0008] Furthermore, the first conductive filler and the second conductive filler are independently selected from at least one of metal nanowires, carbon nanotubes, and conductive polymers, and the volume percentage of the conductive filler is 3% to 7%.

[0009] Furthermore, the collagen aggregates are extracted from any of the following biological sources: mammalian dermal collagen, fish scale collagen, avian skin collagen, and animal tendon collagen.

[0010] Furthermore, the diameter ratio of the core layer to the winding layer is 1.5:1 to 2.5:1, and the elastic modulus of the core layer is 20%-50% higher than that of the winding layer.

[0011] Furthermore, when the axial tensile rate reaches 20%-50%, the transverse diameter expansion rate of the negative Poisson's ratio structure is 5%-15% (initial diameter reference before stretching). The negative Poisson's ratio effect is achieved through the synergistic effect of the helical twist angle (30°~60°) and the difference in elastic modulus of the core layer / winding layer (20%-50%).

[0012] Furthermore, the radial expansion energy generated by the helical structure during axial stretching drives the contact area between the core layer and the winding layer to increase by 20%-50% (based on the initial contact area), thereby achieving dynamic coupling enhancement of the negative Poisson's ratio effect and the triboelectric effect.

[0013] A method for preparing triboelectric sensing yarn based on a negative Poisson's ratio structure includes the following steps: (1) Core layer preparation: Modified polyvinyl chloride (degree of polymerization 1300-1500) is dissolved in tetrahydrofuran to prepare a homogeneous solution with a mass concentration of 10%~20%, and 0.1%~0.5% of epoxidized soybean oil is added as a plasticizer; after the polyvinyl chloride is completely dissolved, 0.01%~0.1% of fluorosilane coupling agent is added in 2-3 gradients, with an interval of 10~15 minutes each time, and mechanically stirred at 800~1200 r / min at 50~60℃ for 20~30 minutes; and degassed by ultrasonic treatment for 30~60 minutes. The fibers, containing 3%–7% conductive filler (silver nanowires: 20–80 nm in diameter; or carbon nanotubes: 5–10 nm in diameter; or polyaniline nanofibers: 50–150 nm in diameter), are extruded through a coaxial spinneret into a gradient ethanol coagulation bath (first zone: 50%–60% ethanol concentration, 25–28°C; second zone: 70%–80% ethanol concentration), with an extrusion rate controlled at 0.5–1.5 mL / min and a pinhole diameter of 0.15–0.75 mm. The fibers are then pre-stretched 1.5–3 times in the coagulation bath (stretching rate 5–10 mm / s), followed by washing 3–5 times in a deionized water bath at 40–50°C with solvent. Finally, the fibers are treated in a hot air circulating drying oven at 70–90°C for 1–2 hours and wound onto a spool to obtain the core yarn. (2) Preparation of the winding layer: 2%~6% cross-linked collagen aggregates are dispersed in deionized water at 45~55℃ and mechanically stirred at 800~1500r / min for 1~2 hours until completely dissolved; 14%~18% polyvinyl alcohol solution is added and stirred at 50~60℃ for 1.5~2.5 hours to form a homogeneous spinning solution; 0.05%~0.1% boric acid is added to the spinning solution and stirred for 20 minutes, then transferred to a defoaming kettle for vacuum degassing (-0.08~-0.1 MPa, 60 minutes), and the pH of the spinning solution is adjusted to 5.5~6.5; 3%~7% conductive filler (silver nanowires: diameter 20~80 nm; or carbon nanotubes: diameter 5~10 nm; or polyaniline nanofibers: diameter 50~150 nm) is added. The mixture (nm) is extruded through a coaxial spinneret into a staged coagulation bath. The first stage coagulation bath is an aqueous solution (30-35℃) containing 3%~5% sodium sulfate and 1%~3% glutaraldehyde, where the spinneret extrudes a fine stream of the original solution (pinhole diameter 0.1~0.3 mm) to complete the initial crosslinking. The second stage coagulation bath is an ethanol-water mixture (40-45℃) containing 28%~32% saturated sodium sulfate and 0.5%~1.5% glutaraldehyde, which achieves in-situ covalent crosslinking of collagen and polyvinyl alcohol. After the nascent fibers are wet-stretched (1.5~2.5 times) by the guide roller group, they enter a phosphate buffer solution (pH 7.4, 50℃) containing 0.1%~0.3% boric acid for wet-heat stretching, while intermittent thermal cycling is applied simultaneously (50℃ / 10 s → room temperature / 20 s). The yarn is first dried in three baths (3-5 times), then washed in deionized water at 45-50°C to remove inorganic salts. Finally, it is wound to obtain the wound layer yarn after being dried in a humidity gradient (first stage: 60%-70% humidity, 60-70°C for 1-2 hours; second stage: 20%-30% humidity, 80-90°C for 1-1.5 hours). (3) Construction of negative Poisson's ratio structure: The core layer and the winding layer yarn are compoundly wound by a precision twisting machine at a spiral angle of 30°~60°, and the linear speed ratio is controlled to be 1:1.2 to 1:1.8 (core layer: winding layer); the yarn tension is monitored in real time during the twisting process to ensure the uniformity of the spiral structure (angle deviation < ±2°); the compound yarn after twisting is placed in a heat treatment box at 80~120℃, axial prestress (0.3~0.8 N) is applied and kept at the temperature for 30~60 minutes to obtain negative Poisson's ratio yarn.

[0014] Compared with the prior art, the effective benefits of the present invention are: (1) The negative Poisson ratio structure triboelectric sensing yarn prepared by the present invention has negative Poisson ratio characteristics. The negative Poisson ratio structure is constructed by spiral winding process, which transforms axial tensile deformation into radial expansion, thereby realizing dynamic coupling enhancement of negative Poisson ratio effect and triboelectric effect.

[0015] (2) The negative Poisson's ratio structure triboelectric sensing yarn prepared by the present invention is biocompatible. It uses collagen-based composite material as positive triboelectric layer and combines conductive core layer encapsulation design to ensure high output performance while meeting the requirements of wearable devices for human contact safety.

[0016] (3) The negative Poisson's ratio structure triboelectric sensing yarn prepared by the present invention has high energy harvesting efficiency, dynamically controls the triboelectric contact area, overcomes the charge dilution problem caused by the attenuation of contact area when traditional triboelectric yarn is stretched, and significantly improves energy conversion efficiency. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the present invention. Figure 2 This is a cross-sectional structural diagram of the present invention. Figure 3 This is a schematic diagram of the negative Poisson's ratio effect stretching of the present invention. Figure 4 This refers to the open-circuit voltage of the present invention under 30% strain conditions. Among them, 1-conductive filler layer, 2-polyvinyl chloride layer, 3-collagen aggregate / polyvinyl alcohol layer Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] like Figure 1 As shown, a triboelectric sensing yarn based on a negative Poisson's ratio structure includes a core layer composed of polyvinyl chloride / conductive filler yarn and an winding layer formed of collagen aggregate / polyvinyl alcohol / electric filler yarn.

[0020] like Figure 2 As shown, a negative Poisson's ratio spiral structure is formed by spiral twisting, and the winding layer covers the outside of the core layer.

[0021] like Figure 3 As shown, the radial spacing of the triboelectric sensing yarn based on the negative Poisson's ratio structure is d3 > d2 > d1 after stretching.

[0022] like Figure 4 As shown, the open-circuit voltage of the triboelectric sensing yarn based on the negative Poisson's ratio structure is 1.25 V under 30% tensile strain. Example

[0023] (1) Core layer preparation: Modified polyvinyl chloride (degree of polymerization 1300) was dissolved in tetrahydrofuran to prepare a homogeneous solution with a mass concentration of 10%, and 0.1% epoxidized soybean oil was added as a plasticizer; after the polyvinyl chloride was completely dissolved, 0.01% fluorosilane coupling agent was added in two gradients, with an interval of 15 minutes between each addition, and mechanically stirred at 800 r / min at 50℃ for 30 minutes; and degassed by ultrasonic treatment for 30 minutes. The 3% silver nanowire ethanol dispersion (diameter 20~80 nm) was extruded through a coaxial spinneret into a gradient ethanol coagulation bath (first zone ethanol concentration 50%, temperature 25℃; second zone ethanol concentration 70%), with the extrusion rate controlled at 0.5 mL / min and the pinhole diameter at 0.15 mm. The fibers were pre-stretched 1.5 times in the coagulation bath (stretch rate 5 mm / s), and then transferred to a 40℃ deionized water bath for washing three times with solvent. After treatment in a 70℃ hot air circulating drying oven for 1 hour, the fibers were finally wound onto a spool to obtain the core yarn.

[0024] (2) Preparation of the winding layer: 2% cross-linked collagen aggregates were dispersed in deionized water at 45℃ and mechanically stirred at 800 r / min for 1 hour until completely dissolved; 14% polyvinyl alcohol solution was added and stirred at 50℃ for 1.5 hours to form a homogeneous spinning solution; 0.05% boric acid was added to the spinning solution and stirred for 20 minutes, then transferred to a defoaming tank for vacuum degassing (-0.08 MPa, 60 minutes), and the pH of the spinning solution was adjusted to 5.5; the mixture was extruded with 3% silver nanowire ethanol dispersion (diameter 20~80 nm) through a coaxial spinneret into a staged coagulation bath. The first stage coagulation bath was an aqueous solution containing 3% sodium sulfate and 1% glutaraldehyde (30℃), and the spinneret extruded a fine stream of the solution (pinhole diameter 0.1 mm). The initial cross-linking of collagen and polyvinyl alcohol is completed in the secondary coagulation bath (40℃) containing 28% saturated sodium sulfate and 0.5% glutaraldehyde. The primary fibers are then wet-stretched (1.5 times) by the guide roller group and then wet-heat stretched in a phosphate buffer solution containing 0.1% boric acid (pH 7.4, 50℃) while being subjected to intermittent thermal cycling (50℃ / 10 s → room temperature / 20 s, 3 times). The fibers are then washed in a three-bath (deionized water, 45℃) to remove inorganic salts. Finally, the fibers are wound after being dried in a humidity gradient (first stage: 60% humidity, 60℃ for 1 hour; second stage: 20% humidity, 80℃ for 1 hour) to obtain the wound layer yarn.

[0025] (3) Construction of negative Poisson's ratio structure: The core layer and the winding layer yarns are compoundly wound at a spiral angle of 30° by a precision twisting machine, and the linear speed ratio is controlled to be 1:1.2 (core layer: winding layer); the yarn tension is monitored in real time during the twisting process to ensure the uniformity of the spiral structure (angle deviation < ±2°); the compound yarn after twisting is placed in an 80°C heat treatment box, axial prestress (0.3 N) is applied and kept warm for 30 minutes to obtain negative Poisson's ratio yarn. Example

[0026] (1) Core layer preparation: Modified polyvinyl chloride (degree of polymerization 1400) was dissolved in tetrahydrofuran to prepare a homogeneous solution with a mass concentration of 15%, and 0.3% epoxidized soybean oil was added as a plasticizer; after the polyvinyl chloride was completely dissolved, 0.05% fluorosilane coupling agent was added in three gradients at 10-minute intervals, and mechanically stirred at 1000 r / min at 55°C for 25 minutes; and degassed by ultrasonic treatment for 45 minutes. The fiber was extruded with 5% carbon nanotube ethanol dispersion (5-10 nm in diameter) through a coaxial spinneret into a gradient ethanol coagulation bath (55% ethanol concentration and 27°C in the first zone; 75% ethanol concentration in the second zone), with the extrusion rate controlled at 1 mL / min and the pinhole diameter at 0.4 mm. The fiber was pre-stretched twice in the coagulation bath (stretch rate 7 mm / s), and then transferred to a 45°C deionized water bath for washing four times with solvent. It was then treated in an 80°C hot air circulating drying oven for 2 hours and finally wound onto a spool to obtain the core yarn.

[0027] (2) Preparation of the winding layer: 4% cross-linked collagen aggregates were dispersed in deionized water at 50℃ and mechanically stirred at 1200 r / min for 2 hours until completely dissolved; 16% polyvinyl alcohol solution was added and stirred at 55℃ for 2 hours to form a homogeneous spinning solution; 0.08% boric acid was added to the spinning solution and stirred for 20 minutes, then transferred to a defoaming tank for vacuum degassing (-0.09 MPa, 60 minutes), and the pH of the spinning solution was adjusted to 6; the mixture was extruded with 5% carbon nanotube ethanol dispersion (diameter 5~10 nm) through a coaxial spinneret into a staged coagulation bath. The first stage coagulation bath was an aqueous solution containing 4% sodium sulfate and 2% glutaraldehyde (33℃), and the spinneret extruded a fine stream of the solution (pinhole diameter 0.2 mm). The initial cross-linking is completed by the first stage (mm); the second stage coagulation bath is an ethanol-water mixture containing 30% saturated sodium sulfate and 1% glutaraldehyde (45℃) to achieve in-situ covalent cross-linking of collagen and polyvinyl alcohol; after the nascent fibers are wet-stretched by the guide roller group (2 times), they are put into a phosphate buffer solution containing 0.2% boric acid (pH 7.4, 50℃) for wet-heat stretching, and intermittent thermal cycling is applied simultaneously (50℃ / 10 s → room temperature / 20 s, 4 times); then the inorganic salts are removed by three-bath washing (deionized water, 50℃); finally, the yarn is wound after being dried by humidity gradient drying (first stage: 65% humidity, 65℃ drying for 1 hour; second stage: 25% humidity, 85℃ drying for 1 hour) to obtain the wound layer yarn.

[0028] (3) Construction of negative Poisson's ratio structure: The core layer and the winding layer yarns are wound together by a precision twisting machine at a spiral angle of 45°, and the linear speed ratio is controlled to be 1:1.5 (core layer: winding layer); the yarn tension is monitored in real time during the twisting process to ensure the uniformity of the spiral structure (angle deviation < ±2°); the twisted composite yarn is placed in a 100°C heat treatment box, axial prestress (0.5N) is applied and kept warm for 45 minutes to obtain negative Poisson's ratio yarn. Example

[0029] (1) Core layer preparation: Modified polyvinyl chloride (degree of polymerization 1500) was dissolved in tetrahydrofuran to prepare a homogeneous solution with a mass concentration of 20%, and 0.5% epoxidized soybean oil was added as a plasticizer; after the polyvinyl chloride was completely dissolved, 0.1% fluorosilane coupling agent was added in three gradients at 10-minute intervals, and mechanically stirred at 1200 r / min at 60°C for 20 minutes; and degassed by ultrasonic treatment for 60 minutes. The polyaniline nanofibers were extruded with a 7% N-methylpyrrolidone dispersion (50-150 nm in diameter) through a coaxial spinneret into a gradient ethanol coagulation bath (60% ethanol concentration and 28°C in the first zone; 80% ethanol concentration in the second zone), with the extrusion rate controlled at 1.5 mL / min and the pinhole diameter at 0.75 mm. The fibers were pre-stretched three times in the coagulation bath (stretch rate 10 mm / s), and then washed five times in a 50°C deionized water bath with solvent. After treatment in a 90°C hot air circulating drying oven for 2 hours, the fibers were finally wound onto a spool to obtain the core yarn.

[0030] (2) Preparation of the winding layer: 6% cross-linked collagen aggregates were dispersed in deionized water at 55℃ and mechanically stirred at 1500 r / min for 2 hours until completely dissolved; 18% polyvinyl alcohol solution was added and stirred at 60℃ for 2.5 hours to form a homogeneous spinning solution; 0.1% boric acid was added to the spinning solution and stirred for 20 minutes, then transferred to a defoaming tank for vacuum degassing (-0.1 MPa, 60 minutes), and the pH of the spinning solution was adjusted to 6.5; the mixture was extruded into a staged coagulation bath with 7% polyaniline nanofiber N-methylpyrrolidone dispersion (diameter 50~150 nm) through a coaxial spinneret. The first stage coagulation bath was an aqueous solution containing 5% sodium sulfate and 3% glutaraldehyde (35℃), and the spinneret extruded a fine stream of the solution (pinhole diameter 0.3 mm). The initial cross-linking of collagen and polyvinyl alcohol is completed by the primary cross-linking bath (mm); the secondary coagulation bath is an ethanol-water mixture containing 32% saturated sodium sulfate and 1.5% glutaraldehyde (45℃) to achieve in-situ covalent cross-linking of collagen and polyvinyl alcohol; after the nascent fibers are wet-stretched by the guide roller group (2.5 times), they are put into a phosphate buffer solution containing 0.3% boric acid (pH 7.4, 50℃) for wet-heat stretching, and intermittent thermal cycling is applied simultaneously (50℃ / 10 s → room temperature / 20 s, 5 times); then the inorganic salts are removed by three-bath washing (deionized water, 50℃); finally, the yarn is wound after being dried by humidity gradient drying (first stage: 70% humidity, 70℃ drying for 2 hours; second stage: 30% humidity, 90℃ drying for 1.5 hours) to obtain the wound layer yarn.

[0031] (3) Construction of negative Poisson's ratio structure: The core layer and the winding layer yarns are compoundly wound at a spiral angle of 60° by a precision twisting machine, and the linear speed ratio is controlled to be 1:1.8 (core layer: winding layer); the yarn tension is monitored in real time during the twisting process to ensure the uniformity of the spiral structure (angle deviation < ±2°); the twisted composite yarn is placed in a 120℃ heat treatment box, axial prestress (0.8N) is applied and kept at the temperature for 60 minutes to obtain negative Poisson's ratio yarn.

Claims

1. A method for preparing a triboelectric sensing yarn based on a negative Poisson's ratio structure, comprising a core layer and a winding layer, wherein the core layer and the winding layer are formed into a core-shell structure by coaxial wet spinning and wound at a helical angle of 30° to 60° by a helical twisting process to form a helical structure with negative Poisson's ratio properties; The core layer is a negative triboelectric layer formed by combining polyvinyl chloride and a first conductive filler. The aforementioned winding layer is a positive triboelectric layer formed by collagen aggregates, polyvinyl alcohol, and a second conductive filler. The diameter ratio of the core layer to the winding layer is 1.5:1 to 2.5:1, and the elastic modulus of the core layer is 20%-50% higher than that of the winding layer. Its features are, The preparation method includes the following steps: (1) Core layer preparation: Modified polyvinyl chloride (PVC) with a degree of polymerization of 1300-1500 was dissolved in tetrahydrofuran to prepare a homogeneous solution with a mass concentration of 10%-20%. 0.1%-0.5% epoxidized soybean oil was added as a plasticizer. After the PVC was completely dissolved, 0.01%-0.1% fluorosilane coupling agent was added in 2-3 gradients, with each addition spaced 10-15 minutes apart, and mechanically stirred at 800-1200 r / min for 20-30 minutes at 50-60°C. After ultrasonic treatment for 30-60 minutes to degas, the fiber was extruded with 3%-7% conductive filler through a coaxial spinneret into a gradient ethanol coagulation bath, controlling the extrusion rate at 0.5-1.5 mL / min and the pinhole diameter at 0.15-0.75 mm. The fiber was then pre-stretched in the coagulation bath at 1.5-3 times its wet state strength, with a stretching rate of 5-10. mm / s, then transferred to a 40~50℃ deionized water bath for washing 3~5 times with solvent; treated in a 70~90℃ hot air circulating drying oven for 1~2 hours, and finally wound onto a bobbin to obtain the core yarn; (2) Preparation of the winding layer: 2%~6% cross-linked collagen aggregates are dispersed in deionized water at 45~55℃ and mechanically stirred at 800~1500 r / min for 1~2 hours until completely dissolved; 14%~18% polyvinyl alcohol solution is added and stirred at 50~60℃ for 1.5~2.5 hours to form a homogeneous spinning solution; 0.05%~0.1% boric acid is added to the spinning solution and stirred for 20 minutes, then transferred to a defoaming tank and vacuum degassed at -0.08~-0.1 MPa for 60 minutes to adjust the pH of the spinning solution to 5.5~6.5; the mixture is extruded with 3%~7% conductive filler through a coaxial spinneret into a staged coagulation bath. The first stage coagulation bath is an aqueous solution containing 3%~5% sodium sulfate and 1%~3% glutaraldehyde at 30~35℃ with a pinhole diameter of 0.1~0.3 mm. The initial cross-linking is achieved by extruding a fine stream of the raw solution through a spinneret at a diameter of mm. The secondary coagulation bath is a mixture of ethanol and water at 40-45℃ containing 28%-32% saturated sodium sulfate and 0.5%-1.5% glutaraldehyde, which enables in-situ covalent cross-linking of collagen and polyvinyl alcohol. After the nascent fibers are wet-stretched to 1.5-2.5 times by the guide roller group, they are placed in a phosphate buffer solution at pH 7.4 containing 0.1%-0.3% boric acid at 50℃ for wet-heat stretching, while intermittent thermal cycling is applied simultaneously: 50℃ / 10 s → room temperature / 20 s, 3-5 times. Subsequently, inorganic salts are removed by three-bath washing with deionized water at 45-50℃. Finally, the yarn is wound after humidity gradient drying to obtain the wound layer yarn. (3) Construction of negative Poisson's ratio structure: The core layer and the winding layer yarn are compoundly wound by a precision twisting machine at a spiral angle of 30°~60°, and the linear speed ratio is controlled to be 1:1.2 to 1:1.8 between the core layer and the winding layer. The yarn tension is monitored in real time during the twisting process to ensure the uniformity of the spiral structure and the angle deviation is <±2°. The twisted composite yarn is placed in a heat treatment box at 80~120℃, and an axial prestress of 0.3~0.8 N is applied and kept at the temperature for 30~60 minutes to obtain the negative Poisson's ratio yarn.

2. The method for preparing a triboelectric sensing yarn based on a negative Poisson's ratio structure according to claim 1, characterized in that, The first and second conductive fillers are independently selected from one of metal nanowires, carbon nanotubes, and conductive polymers, and the volume percentage of the conductive fillers is 3% to 7%.

3. The method for preparing a triboelectric sensing yarn based on a negative Poisson's ratio structure according to claim 1, characterized in that, The collagen aggregates are extracted from any of the following biological sources: mammalian dermal collagen, fish scale collagen, avian skin collagen, and animal tendon collagen.

4. The method for preparing a triboelectric sensing yarn based on a negative Poisson's ratio structure according to claim 1, characterized in that, The conductive filler is silver nanowire, carbon nanotube or polyaniline nanofiber, with silver nanowire having a diameter of 20~80nm; carbon nanotube having a diameter of 5~10nm; and polyaniline nanofiber having a diameter of 50~150nm.

5. The method for preparing a triboelectric sensing yarn based on a negative Poisson's ratio structure according to claim 1, characterized in that, The gradient ethanol coagulation bath has an ethanol concentration of 50%~60% and a temperature of 25~28℃ in the first gradient zone and an ethanol concentration of 70%~80% in the second gradient zone.

6. The method for preparing a triboelectric sensing yarn based on a negative Poisson's ratio structure according to claim 1, characterized in that, The humidity gradient drying process includes a first gradient stage of 60%~70% humidity and 60~70℃ for 1~2 hours; and a second gradient stage of 20%~30% humidity and 80~90℃ for 1~1.5 hours.

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